This invention relates to an image pickup apparatus which picks up images of an image pickup object, for example, of a celestial hemispheric space over a wide range and stitches the images to each other to form a single image with a reduced parallax between the images.
Various camera apparatus have been developed wherein a large number of video cameras are accommodated in a housing and simultaneously pick up an image omnidirectionally or over an overall circumference.
For example, as shown in FIG. 1, in order to image, in a horizontal plane about a certain point in space selected as a viewpoint, and to obtain an image over a wide angle such as a panorama image about the selected viewpoint, a plurality of cameras 1, 2, . . . are disposed at equal distances in a circumferential direction along a circle centered at the viewpoint 1. The cameras are fixed with optical axes 3, 4, . . . of lenses 1a, 2a, . . . of the cameras 1, 2, . . . directed in radial directions as seen in FIG. 1. Then, individual images picked up by the cameras 1, 2, . . . are stitched together at positions over which they overlap with each other to allow image pickup over the overall circumference. Image pickup elements 5, 6, . . . such as CCDs are provided at the rear ends of the cameras 1, 2, . . . , rearwardly of the lenses 1a, 2a. 
When the individual images picked up by the cameras 1, 2, . . . are stitched to as described above, a parallax is likely to appear at such overlapping locations. Thus, it is a technical subject in a picked up image processing technique how the parallax is reduced.
In conventional image pickup apparatus, however, the cameras 1, 2, . . . are located at positions at which each of them simply picks up an image of part of the image pickup object, and no particular countermeasure for solving the problem of the parallax described above is provided.
As a result, the parallax makes an obstacle to stitching of overlapping locations of picked up images after the image pickup is completed, and the images cannot be stitched well into a good image.
Further, in conventional image pickup apparatus, lens barrels of the cameras are physically restricted in terms of the arrangement relative to each other, and it is difficult to arrange the cameras in a closely neighboring relationship to each other. Therefore, a parallax is liable to appear between images picked up by the cameras.
Since the value of the parallax varies depending upon the distance from a camera to an image pickup object, when picked up images are stitched together after completion of the image pickup, an image obtained by the stitching varies depending on the position of an image in the overlapping region which is used as a reference for the stitching.
In particular, in order to carry out practical stitching of images which have a parallax, it is necessary for an editor to observe the images and determine what portion of the images is significant and then determine the position of that portion as a reference. This makes it difficult to automate the stitching of moving pictures, and creates a significant obstacle to the automation of processing of picked up images.